Twin skeg ship

ABSTRACT

Provided is a twin skeg ship equipped with a pair of left and right skegs provided at a bottom of a stern, propellers provided behind the pair of left and right skegs; and fins provided in front of the propellers only at inner sides in a ship width direction with respect to the skegs and configured to radially extend from rotational centers of the propellers.

TECHNICAL FIELD

The present invention relates to a twin skeg ship having propellershafts at a pair of left and right skegs provided on the bottom of astern.

Priority is claimed on Japanese Patent Applications No. 2014-233257,filed on Nov. 18, 2014, the contents of which are incorporated herein byreference.

BACKGROUND ART

A twin skeg ship in which a pair of left and right skegs are provided onthe bottom of a stern to form a tunnel-shaped bottom recess between theleft and right skegs and propeller shafts for the pair of left and rightskegs are provided is known.

In such a twin skeg ship, various proposals have been presented toimprove propulsion performance.

A constitution in which a fin extending in a leftward/rightwarddirection is provided between left and right skegs is disclosed in, forexample, Patent Literature 1. In this constitution, a flow passingthrough an upper portion of a tunnel, both sides of which are surroundedby the skegs, hits the fin between the left and right skegs, and therebygenerates a lift force to improve the propulsion performance using partof the lift force as an advance force.

A constitution in which fins are provided on inner wall surfaces of apair of left and right skegs is also disclosed in Patent Literature 2.This fin is provided to have an elevation angle with respect to alongitudinal vortex generated between the left and right skegs.According to this constitution, as the longitudinal vortex hits the fin,a lift force having an advance directional component occurs, and thusthe propulsion performance is improved by the advance directionalcomponent.

A constitution in which a tubular duct having a greater diameter at abow side than at a stern side is provided in front of a propeller isdisclosed in Patent Literature 3. According to this constitution, thetubular duct straightens a flow of the propeller to improve propulsionperformance.

CITATION LIST Patent Literature [Patent Literature 1]

Japanese Patent No. 5426699

[Patent Literature 2]

Japanese Unexamined Patent Application, First Publication No.2012-006556

[Patent Literature 3]

Japanese Unexamined Patent Application, First Publication No.2008-143488

SUMMARY OF INVENTION Technical Problem

Various proposals have been given to improve the propulsion performance.However, the flow below the bottom is variously changed by a shape ofthe stern bottom of the hull. As a result, even if such constitutions asdisclosed in, for instance, Patent Literatures 1 to 3 are applied, thepropulsion performance is not always improved, but may actually bereduced. Thus, further improvement in the propulsion performance isalways required.

The present invention is directed to providing a twin skeg ship capableof improving propulsion performance.

Solution to Problem

According to a first aspect of the present invention, a twin skeg shipincludes: a pair of left and right skegs provided at a bottom of astern; propellers provided behind the pair of left and right skegs; andfins provided in front of the propellers only at inner sides in a shipwidth direction with respect to the skegs and configured to radiallyextend from rotational centers of the propellers.

In this way, as the fins are provided in front of the propellers only atthe inner sides in the ship width direction with respect to the skegs,flows at the inner sides of the skegs in the ship width direction can bestrengthened or weakened in front of the propellers by the fins.Thereby, the wake gain can be increased in the left and rightpropellers.

In the twin skeg ship, flows at the inner sides in the ship widthdirection with respect to the skegs may be configured to be slower thanflows at outer sides in the ship width direction with respect to theskegs.

In the twin skeg ship having this constitution, specific resistance ofthe fins provided only at the inner sides of the skegs in the ship widthdirection can be reduced, and as the slow flows at the inner sides ofthe skegs in the ship width direction are accelerated or decelerated infront of the propellers by the fins, it is possible to effectivelyincrease the wake gains of the propellers to improve the propulsionperformance.

In the twin skeg ship, the fins may be configured to strengthen upwardflows occurring at the inner sides of the skegs in the ship widthdirection in front of the propellers in the pair of left and rightskegs.

In this way, as the fins are provided in regions in which the upwardflows occurring at the inner sides of the skegs in the ship widthdirection are strengthened, it is possible to effectively increase thewake gains of the propellers to improve the propulsion performance.

In the twin skeg ship, rotating directions of the propellers may be setto be inward directions in which upper portions of the propellers rotatefrom the outer sides in the ship width direction toward the inner sidesin the ship width direction.

According to this constitution, the upward flows that are strengthenedby the fins and occur at the inner sides of the skegs in the ship widthdirection cause strong flows in directions opposite to the rotatingdirections of the propellers. Therefore, it is possible to effectivelyincrease the wake gains of the propellers to improve the propulsionperformance.

In the twin skeg ship, the fins may be configured to weaken upward flowsoccurring at the inner sides of the skegs in the ship width direction infront of the propellers in the pair of left and right skegs.

In this way, as the fins are provided in regions in which the upwardflows occurring at the inner sides of the skegs in the ship widthdirection are weakened, it is possible to effectively increase the wakegains of the propellers to improve the propulsion performance.

In the twin skeg ship, rotating directions of the propellers may be setto be outward directions in which upper portions of the propellersrotate from the inner sides in the ship width direction toward the outersides in the ship width direction.

According to this constitution, even when the upper portions of thepropellers rotate outward from the inner sides in the ship widthdirection toward the outer sides in the ship width direction, the flowsat the inner sides of the skegs in the ship width direction are weakenedin front of the propeller by the fins, and thereby flows in the samedirections as the rotating directions of the propellers are weakened,and it is possible to increase the wake gains to improve the propulsionperformance in the left and right propellers.

The twin skeg ship may be configured to further include tubular ductswhich are provided in front of the propellers while crossing the innersides of the skegs in the ship width direction and the outer sides ofthe skegs in the ship width direction and whose outer diameters aregradually reduced from a bow side toward a stern side.

With this constitution, flows directed to the propellers are acceleratedby passing through the inside of the ducts. Thereby, since a propulsiveforce in an advance direction occurs at the ducts, the propulsionperformance can be increased.

The twin skeg ship may be configured to further include semi-cylindricalducts which are in front of the propellers and are provided only at theinner sides in the ship width direction with respect to the skegs andwhose outer diameters are gradually reduced from a bow side toward astern side.

With this constitution, the flows directed to the propellers areaccelerated by passing through the inside of the ducts. Thereby, since apropulsive force in an advance direction occurs, the propulsionperformance can be increased. Thus, according to the constitution, noducts are present at the outer sides of the skegs in the ship widthdirection. Therefore, in comparison with a case in which the ducts areexposed to the outer sides of the skegs in the ship width direction,specific resistance caused by the ducts can be reduced. As a result, apropulsive force caused by the ducts can be increased to moreeffectively improve the propulsion performance.

In the twin skeg ship, the ducts may be configured to be supported onends of outer circumferential sides of the fins or on intermediateportions of the fins.

Advantageous Effects of Invention

According to the twin skeg ship of the present invention, the flows atthe inner sides in the ship width direction are accelerated ordecelerated with respect to the skegs by the fins, and the wake gains ofthe propellers are increased. Thereby, the propulsion performance can beimproved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a left side view of a starboard side at a stern portion of atwin skeg ship of a first embodiment of the present invention whenviewed from a port side.

FIG. 2 is a rear view of the stern portion of the twin skeg ship whenviewed from the rear, and is a view showing cross sections D1-D1, D2-D2,D3-D3, and D4-D4 of FIG. 1.

FIG. 3 is a view showing a result of fully analyzing a flow fieldimmediately in front of a propeller of the port side of a certain twinskeg ship in which a pair of left and right propellers rotate inwardwhen viewed from a stern side.

FIG. 4 is a rear view of the stern portion of the twin skeg ship in amodification of the first embodiment of the present invention whenviewed from the rear.

FIG. 5 is a left side view of a starboard side at a stern portion of atwin skeg ship of a second embodiment of the present invention whenviewed from a port side.

FIG. 6 is a rear view of the stern portion of the twin skeg ship shownin FIG. 5 when viewed from the rear.

FIG. 7 is a left side view of a starboard side at the stern portion ofthe twin skeg ship in a modification of the second embodiment of thepresent invention when viewed from a port side.

FIG. 8 is a rear view of the stern portion of the twin skeg ship shownin FIG. 7 when viewed from the rear.

FIG. 9 is a rear view of a stern portion of a twin skeg ship of a thirdembodiment of the present invention when viewed from the rear.

FIG. 10 is a rear view of the stern portion of the twin skeg ship in amodification of the third embodiment of the present invention whenviewed from the rear.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a twin skeg ship of an embodiment of the present inventionwill be described based on the drawings.

First Embodiment

FIG. 1 is a left side view of a starboard side at a stern portion of atwin skeg ship of a first embodiment of the present invention whenviewed from a port side. FIG. 2 is a rear view of the stern portion ofthe twin skeg ship when viewed from the rear.

As shown in FIGS. 1 and 2, the twin skeg ship 1 is equipped with skegs 2and propellers 10.

A stern hull 3 that is a stern 1 b of a hull of the twin skeg ship 1 hasinclined surfaces 4 s at which a bottom 4 thereof is gradually inclinedupward from the side of a bow (not shown) toward the side of the stern 1b. Also, the bottom 4 of the stern hull 3 is formed such that a widthdimension in a ship width direction is gradually reduced from the sideof the bow (not shown) toward the side of the stern 1 b.

The pair of left and right skegs 2 are symmetrically provided oninclined surfaces 4 s of the bottom 4 across an inner side C in the shipwidth direction at an interval in the ship width direction. The pair ofleft and right skegs 2 are each provided in a shape that extendsdownward from the inclined surface 4 s of the bottom 4 of the stern hull3 to protrude backward from the inclined surface 4 s in a horizontaldirection.

A bottom recess 5 surrounded by the pair of left and right skegs 2 andthe inclined surfaces 4 s of the bottom 4 is formed below the stern hull3 by the pair of left and right skegs 2 and the inclined surfaces 4 s ofthe bottom 4. The bottom recess 5 is formed such that a cross-sectionalarea thereof is gradually reduced toward the stern 1 b.

Also, rear ends of the skegs 2 are each provided with a tubular bossing6 protruding backward.

The propellers 10 are provided at the rear ends of the pair of left andright skegs 2. Each of the propellers 10 is connected to a main machine(not shown) provided inside the stern hull 3 via a propeller shaft 12.The propeller shaft 12 is connected to the main machine (not shown)inside the stern hull 3 at one end thereof, extends toward the stern 1 bat the other end 12 b thereof, and protrudes from the inside of thestern hull 3 through the bossing 6 and behind the skeg 2. The propellers10 are integrally mounted on the other ends 12 b of the propeller shafts12 protruding behind the skegs 2.

The propeller shafts 12 are driven to rotate about central axes thereofby the main machine (not shown) provided inside the stern hull 3, andthereby the propellers 10 rotate in a predetermined direction to exert apropulsive force of the twin skeg ship 1.

In this embodiment, rotating directions of the propellers 10 provided atthe rear ends of the pair of left and right skegs 2 are set to turn ininward directions R2 and R1 in which upper portions of the propellers 10rotate from the outer sides in the ship width direction toward the innersides C in the ship width direction.

Fins 20 are provided in front of the pair of left and right propellers10. A plurality of fins 20 (e.g., three fins in the present embodiment)are provided on an outer circumferential surface of each of the bossings6, which are provided to protrude backward from the rear ends of theskegs 2 to radially protrude from the rotational center of each of thepropellers 10.

In this embodiment, the fins 20 are provided close to the inner sides Cin the ship width direction with respect to the pair of left and rightskegs 2. That is, the fins 20 are provided to protrude from an outercircumferential surface 6 s of the bossing 6, which is close to theinner side C in the ship width direction, to a space inside the bottomrecess 5.

The fins 20 cause flows F1 and F2 in directions opposite to the rotatingdirections of the propellers 10 located therebehind, that is, in outwarddirections in which the upper portions of the propellers 10 are directedfrom the vicinities of the inner sides C in the ship width directiontoward the outer sides in the ship width direction.

Incidentally, in the twin skeg ship 1, due to the shape of the bottom 4of the stern hull 3, the flow velocity in the bottom recess 5 formedbetween the pair of left and right skegs 2 is slower than flows of outersides (outer sides in the ship width direction) of the pair of left andright skegs 2.

FIG. 3 is a view showing a result of fully analyzing a flow fieldimmediately in front of the propeller 10 of the port side in the skeg 2of the port side of the twin skeg ship 1 in which the pair of left andright propellers 10 turn inward at upper sides thereof. In FIG. 3, thedirections of arrows indicate directions of flows within planes thereof,the lengths of the arrows indicate magnitudes of the flows, and a circleindicates the radius of rotation of the propeller 10.

As shown in FIG. 3, an upward flow Fs becoming a flow in a directionopposite to a rotating direction R2 of the propeller 10 is generatedclose to the inner side C in the ship width direction, i.e., within arange of θ=00 to 900 and 90° to 180° with respect to the skeg 2 of theport side.

The fins 20 provided close to the inner side C in the ship widthdirection with respect to the skeg 2 are provided in a region in whichthe upward flow Fs occurs in the direction opposite to the rotatingdirection R2 of the propeller 10.

Thereby, the fins 20 of the port side cause the flow F2 in the outwarddirection at the upper portion of the propeller 10, which is thedirection opposite to the rotating direction of the propeller 10 locatedtherebehind, thereby accelerating and strengthening the upward flow Fsbecoming the flow that is in the direction opposite to the rotatingdirection R2 of the propeller 10 and occurs in front of the propeller 10of the port side. Also, the fins 20 of the starboard side cause the flowF1 in the outward direction at the upper portion of the propeller 10,which is the direction opposite to the rotating direction of thepropeller 10 located therebehind, thereby strengthening the upward flowFs becoming a flow that is in a direction opposite to the rotatingdirection R1 of the propeller 10 and occurs in front of the propeller 10of the starboard side.

The upward flows Fs which occur in front of the left and rightpropellers 10 and whose directions are opposite to the rotatingdirections R1 and R2 of the propellers 10 are strengthened by the abovefins 20, and thereby the wake gain increases in the left and rightpropellers 10.

Therefore, according to the twin skeg ship of the first embodimentmentioned above, the fins 20 radially extending only toward the innersides C in the ship width direction with respect to the skegs 2 areprovided in front of the pair of left and right propellers 10. Due tothese fins 20, the flows close to the inner sides C in the ship widthdirection in the skegs 2 can be strengthened in front of the propellers10. Thereby, since the wake gain can be increased in the left and rightpropellers 10, it is possible to efficiently collect the flows toimprove the propulsion performance.

In particular, in the twin skeg ship 1, the flows Fs close to the innersides C in the ship width direction with respect to the skegs 2 are slowdue to the flows at the outer side in the ship width direction withrespect to the skegs 2. In the twin skeg ship 1 having thisconstitution, specific resistance of the fins 20 can be reduced, and theslow flows Fs at the inner sides C of the skegs 2 in the ship widthdirection are accelerated in front of the propellers 10 by the fins 20.Thereby, it is possible to effectively increase the wake gain of thepropellers 10 to improve the propulsion performance.

Further, the fins 20 are provided in the region in which the upwardflows Fs occurring close to the inner sides C of the skegs 2 in the shipwidth direction are strengthened. Thereby, it is possible to effectivelyincrease the wake gain of the propellers 10 to improve the propulsionperformance.

Also, the rotating directions of the propellers 10 are set to be inwarddirections in which the upper portions of the propellers 10 rotate fromthe outer sides in the ship width direction toward the inner sides C inthe ship width direction. According to this constitution, the upwardflows Fs that occur close to the inner sides C of the skegs 2 in theship width direction are strengthened in front of the propellers 10 bythe fins 20, and become the directions opposite to the rotatingdirections of the propellers 10. Therefore, in the left and rightpropellers 10 rotating in the inward directions, it is possible toeffectively increase the wake gain of the propellers 10 to improve thepropulsion performance.

(Modification of the First Embodiment)

FIG. 4 is a rear view of the stern portion of the twin skeg ship in amodification of the first embodiment of the present invention whenviewed from the rear.

In the first embodiment, the upper portions of the left and rightpropellers 10 are designed to rotate in the inward directions, but theyare not limited thereto. As shown in FIG. 4, even in the constitution inwhich the upper portions of the left and right propellers 10 rotate inthe outward directions, similar to the above embodiment, the fins 20 maybe radially provided close to the inner sides C in the ship widthdirection with respect to the pair of left and right skegs 2.

According to this constitution, since a flow in the same outwarddirection in which the propeller 10 rotates can be weakened by the fins20, it is possible to increase the wake gain to improve the propulsionperformance.

Second Embodiment

Next, a second embodiment of the twin skeg ship of the present inventionwill be described. In the second embodiment described below, since theonly difference from the first embodiment is that ducts 30 are alsoprovided, portions that are the same as those of the first embodimentwill be given the same symbols, and duplicate description thereof willbe omitted.

FIG. 5 is a left side view of a starboard side at a stern portion of thetwin skeg ship of the second embodiment of the present invention whenviewed from a port side. FIG. 6 is a rear view of the stern portion ofthe twin skeg ship shown in FIG. 5 when viewed from the rear.

As shown in FIGS. 5 and 6, the twin skeg ship 1 in this embodiment isequipped with, similar to the first embodiment, a pair of left and rightskegs 2 and a pair of left and right propellers 10.

Thus, rotating directions of the propellers 10 provided at rear ends ofthe pair of left and right skegs 2 are set to be inward directions R2and R1 in which upper portions of the propellers 10 rotate from outersides in a ship width direction toward inner sides C in the ship widthdirection.

Fins 20 are provided in front of the pair of left and right propellers10. The fins 20 are radially provided to protrude from an outercircumferential surface 6 s of a bossing 6 which is close to the innerside C in the ship width direction to a space inside a bottom recess 5.

These fins 20 cause flows F1 and F2 in directions opposite to therotating directions of the propellers 10 located therebehind, that is,in outward directions in which the upper portions of the propellers 10are directed from the vicinities of the inner sides C in the ship widthdirection toward the outer sides in the ship width direction.

Further, in this embodiment, tubular ducts 30 are provided in front ofthe propellers 10. Each of the ducts 30 is concentrically disposedcentering on the bossing 6 in a cylindrical shape formed in a circularshape when viewed from the side of a stern 1 b.

The duct 30 is fixed to ends of outer circumferential sides of aplurality of fins 20 that radially extend from the bossing 6, andthereby is supported on the ends. That is, the duct 30 uses theplurality of fins 20 as support members, and is fixed to the bossing 6.

The duct 30 is formed in a tapered shape such that an outer diameterthereof is gradually reduced from the side of a bow to the side of thestern 1 b. Also, the lengths of the ducts 30 in a ship length directionare set to be the same in a circumferential direction.

According to this constitution, upward flows Fs which occur in front ofthe propellers 10 and whose directions are opposite to the rotatingdirections R1 and R2 of the propellers 10 are strengthened by the fins20 provided close to the inner sides C in the ship width direction withrespect to the skegs 2, and thereby a wake gain increases in the leftand right propellers 10.

Further, since the outer diameter of the duct 30 is gradually reducedtoward the propeller 10 close to the stern 1 b, the flow velocity insidethe duct 30 is increased in the vicinity of the stern 1 b. Therefore, apropulsive force in an advance direction occurs in the duct 30.

Therefore, according to the twin skeg ship of the aforementioned secondembodiment, similar to the first embodiment, flows close to the innersides C in the ship width direction in the skegs 2 can be strengthenedin front of the propellers 10 by the fins 20 provided in front of thepair of left and right propellers 10. Thereby, it is possible toincrease the wake gain in the left and right propellers 10, and toefficiently collect the flows to improve propulsion performance.

Also, the twin skeg ship in this embodiment is equipped with the tubularducts 30 whose outer diameters are gradually reduced from the side ofthe bow toward the side of the stern 1 b to cross the vicinities of theinner sides C and the outer sides of the skegs 2 in the ship widthdirection in front of the propellers 10. The flows passing through theinsides of the ducts 30 to thereby flow toward the propellers 10 areaccelerated. Thereby, since the propulsive force in the advancedirection occurs at the ducts 30, the propulsion performance can beenhanced.

(Modification of the Second Embodiment)

FIG. 7 is a left side view of a starboard side at the stern portion ofthe twin skeg ship in a modification of the second embodiment of thepresent invention when viewed from a port side. FIG. 8 is a rear view ofthe stern portion of the twin skeg ship shown in FIG. 7 when viewed fromthe rear.

In the second embodiment, as the ducts 30 are fixed to the ends of theouter circumferential sides of the plurality of fins 20, the ducts 30are designed to have the same diameters as the outer circumferentialsides of the plurality of fins 20, but are not limited thereto.

As shown in FIGS. 7 and 8, the ducts 30 may be designed to have smallerdiameters than the outer circumferential sides of the plurality of fins20, and to be fixed by intermediate portions of the plurality of fins20.

Even in the modification of this second embodiment, similar to thesecond embodiment, the propulsion performance can be improved.

Third Embodiment

Next, a third embodiment of the twin skeg ship of the present inventionwill be described. In the third embodiment described below, since theonly difference from the second embodiment is the constitutions of ducts40, the portions that are the same as those of the second embodimentwill be given the same symbols, and duplicate description thereof willbe omitted.

FIG. 9 is a rear view of the stern portion of the twin skeg ship of thethird embodiment of the present invention when viewed from the rear.

As shown in FIG. 9, the twin skeg ship 1 in this embodiment is equippedwith, similar to the first and second embodiments, a pair of left andright skegs 2 and a pair of left and right propellers 10.

Thus, rotating directions of the propellers 10 provided at rear ends ofthe pair of left and right skegs 2 are set to be inward directions R2and R1 in which upper portions of the propellers 10 rotate from outersides in a ship width direction toward inner sides C in the ship widthdirection.

Fins 20 are provided in front of the pair of left and right propellers10. The fins 20 are radially provided to protrude from an outercircumferential surface 6 s of a bossing 6, which is close to the innerside C in the ship width direction, to a space inside a bottom recess 5.

These fins 20 cause flows F1 and F2 in directions opposite to therotating directions of the propellers 10 located therebehind, that is,in outward directions in which the upper portions of the propellers 10are directed from the vicinities of the inner sides C in the ship widthdirection toward the outer sides in the ship width direction.

Further, in this embodiment, semi-cylindrical ducts 40 are provided infront of the propellers 10. Each of the ducts 40 is concentricallydisposed centering on the bossing 6 at the inner side C in the shipwidth direction in a cylindrical shape formed in a semicircular shapewhen viewed from the side of a stern 1 b.

The duct 40 is fixed to ends of outer circumferential sides of aplurality of fins 20 that radially extend from the bossing 6, andthereby is supported on the ends. That is, the duct 40 uses theplurality of fins 20 as support members, and is fixed to the bossing 6.

The duct 40 is formed in a tapered shape such that an outer diameter ofcurvature of an outer circumferential surface thereof is graduallyreduced from the side of a bow toward the side of the stern 1 b. Also,the lengths of the ducts 40 in a ship length direction are set to be thesame in a circumferential direction.

According to this constitution, upward flows Fs which occur in front ofthe propellers 10 and whose directions are opposite to the rotatingdirections R1 and R2 of the propellers 10 are strengthened by the fins20 provided close to the inner sides C in the ship width direction withrespect to the skegs 2, and thereby the wake gain increases in the leftand right propellers 10.

Further, since the outer diameter of the duct 40 is gradually reducedtoward the propeller 10 close to the stern 1 b, flows at wake sides ofthe skegs 2 are accelerated close to the inner sides C in the ship widthdirection with respect to the skegs 2. Therefore, a propulsive force inan advance direction occurs in the duct 40.

Therefore, according to the twin skeg ship of the aforementioned thirdembodiment, similar to the first and second embodiments, flows close tothe inner sides C in the ship width direction in the skegs 2 can bestrengthened in front of the propellers 10 by the fins 20 provided infront of the pair of left and right propellers 10. Thereby, it ispossible to increase the wake gain in the left and right propellers 10,and to efficiently collect the flows to improve propulsion performance.

Also, the twin skeg ship in this embodiment is equipped with thesemi-cylindrical ducts 40 whose outer diameters are gradually reducedfrom the side of the bow toward the side of the stern 1 b only in thevicinities of the inner sides C of the skegs 2 in the ship widthdirection in front of the propellers 10. The flows passing through theinsides of the ducts 40 to thereby flow toward the propellers 10 areaccelerated. Thereby, since the propulsive force in the advancedirection occurs at the ducts 40, the propulsion performance can beenhanced.

In addition, according to this constitution, no ducts 40 are present atthe outer sides of the skegs 2 in the ship width direction. Incomparison with the case in which the ducts 30 are exposed to the outersides of the skegs 2 in the ship width direction as in the secondembodiment, specific resistance caused by the ducts 40 can be reduced.As a result, the propulsive force caused by the ducts 40 can be furtherincreased, and the propulsion performance can be more efficientlyimproved.

(Modification of the Third Embodiment)

FIG. 10 is a rear view of the stern portion of the twin skeg ship in amodification of the third embodiment of the present invention whenviewed from the rear.

In the third embodiment, as the ducts 40 are fixed to the ends of theouter circumferential sides of the plurality of fins 20, the ducts 40are designed to have the same diameters as the outer circumferentialsides of the plurality of fins 20, but are not limited thereto.

As shown in FIG. 10, the ducts 40 may be designed to have smallerdiameters than the outer circumferential sides of the plurality of fins20, and to be fixed by intermediate portions of the plurality of fins20.

Even in the modification of this third embodiment, similar to the thirdembodiment, the propulsion performance can be improved.

(Other Modifications)

The prevent invention is not limited to the aforementioned embodiments,and also includes various modifications of the aforementionedembodiments that do not depart from the spirit and scope of the presentinvention. That is, the specific shapes and constitutions represented inthe embodiments are merely examples, and can be appropriately modified.

For example, in each of the embodiments and their modifications, theplurality of fins 20 are radially provided, but there is no limitationon the number installed or the angle at which they are installed.

Also, the ducts 30 and 40 are provided at the outer circumferentialportions of the fins 20 in the second and third embodiments, but theducts 30 and 40 may be separately provided while their positions areshifted from the fins 20 in the ship length direction.

REFERENCE SIGNS LIST

-   -   1: twin skeg ship    -   1 b: stern    -   2: skeg    -   3: stern hull    -   4: bottom    -   4 s: inclined surface    -   5: bottom recess    -   6: bossing    -   6 s: outer circumferential surface    -   10: propeller    -   12: propeller shaft    -   12 b: other end    -   21    -   20: fin    -   30: duct    -   40: duct    -   C: inner side in ship width direction    -   R1, R2: rotating direction

1. A twin skeg ship comprising: a pair of left and right skegs providedat a bottom of a stern; propellers provided behind the pair of left andright skegs; and fins provided in front of the propellers only at innersides in a ship width direction with respect to the skegs and configuredto radially extend from rotational centers of the propellers.
 2. Thetwin skeg ship according to claim 1, wherein flows at the inner sides inthe ship width direction with respect to the skegs are slower than flowsat outer sides in the ship width direction with respect to the skegs inthe pair of left and right skegs.
 3. The twin skeg ship according toclaim 1, wherein the fins strengthen upward flows occurring at the innersides of the skegs in the ship width direction in front of thepropellers.
 4. The twin skeg ship according to claim 1, wherein rotatingdirections of the propellers are set to be inward directions in whichupper portions of the propellers rotate from the outer sides in the shipwidth direction toward the inner sides in the ship width direction. 5.The twin skeg ship according to claim 1, wherein the fins weaken upwardflows occurring at the inner sides of the skegs in the ship widthdirection in front of the propellers.
 6. The twin skeg ship according toclaim 1, wherein rotating directions of the propellers are set to beoutward directions in which upper portions of the propellers rotate fromthe inner sides in the ship width direction toward the outer sides inthe ship width direction.
 7. The twin skeg ship according to claim 1,further comprising tubular ducts which are provided in front of thepropellers while crossing the inner sides of the skegs in the ship widthdirection and the outer sides of the skegs in the ship width directionand whose outer diameters are gradually reduced from a bow side toward astern side.
 8. The twin skeg ship according to claim 1, furthercomprising semi-cylindrical ducts which are provided in front of thepropellers only at the inner sides of the skegs in the ship widthdirection and whose outer diameters are gradually reduced from a bowside toward a stern side.
 9. The twin skeg ship according to claim 7,wherein the ducts are supported on ends of outer circumferential sidesof the fins or on intermediate portions of the fins.